Tooth enamel is a porous material. Consequently, it can become discoloured as a result of exposure to coloured materials. Examples of such materials include the pigments produced by oral microbes, and pigments found in foodstuffs, beverages, tobacco products, and medicaments. Discoloured teeth are widely considered to be cosmetically unattractive. There is therefore significant consumer demand for oral care compositions with tooth whitening properties.
A number of methods for whitening teeth are known. Of these, the use of tooth-whitening toothpastes is perhaps the most common; most whitening toothpastes can be administered by consumers without the intervention of a dental professional. Whitening toothpastes typically comprise an abrasive, which polishes the teeth when applied by brushing. The abrasive must be carefully selected. The abrasive must produce a whitening effect without damaging the tooth enamel.
Certain common abrasives, such as calcium carbonate, have relatively low abrasiveness. While they may contribute to the cleaning of teeth, they fail to produce an appreciable whitening effect. In contrast, many silicas are relatively strong abrasives and are desirably incorporated into tooth whitening formulations. Slicas are known to interact with some functional ingredients, particularly metal ions such as zinc (II). Antimicrobial ingredients are useful for the treatment or prevention of other oral diseases or disorders, including dental caries and periodontal disease, and are commonly included in oral care compositions. Since oral bacteria can contribute to tooth discolouration, it is desirable to incorporate antimicrobial ingredients into tooth whitening products.
Zinc compounds are a particularly useful class of antimicrobial ingredients. Zinc has been shown to fight plaque, to prevent the formation of dental calculus, and to reduce mouth malodour. Zinc can also aid in the treatment and prevention of tooth hypersensitivity. While zinc offers many oral health benefits, its organoleptic characteristics are poor. It is therefore desirable to reduce the levels of zinc used in oral care compositions, while still providing oral health benefits. This would improve consumer acceptance of oral care compositions comprising zinc. A further aim is to provide a tooth whitening composition comprising a reduced concentration of zinc while maintaining high antimicrobial efficacy.
In a first aspect, the present invention provides a dentifrice comprising zinc compounds and abrasives, wherein the abrasives comprises abrasive silica and calcium carbonate, and wherein the composition is a tooth whitening and enamel strengthening composition.
Optionally, the pH of the composition is at least 7.0.
Optionally, the pH of the composition is in the range pH 9.4 to 10.0.
Optionally, the abrasive is present in an amount in the range 10% to 45% by weight of the composition.
Optionally, the abrasive is present in an amount in the range 25% to 45% by weight of the composition.
Optionally, the zinc compound is present in the composition in an amount in the range of about 0.1 wt % to about 5 wt % by weight of the composition. The amount of zinc ions in the specification can also be characterized by the corresponding percentage weight of the zinc ions relative to the zinc compound (e.g. about 0.1 wt % to about 5 wt % of zinc oxide corresponds to about 0.08 wt % to 4.02 wt % of zinc ions).
Optionally, the calcium carbonate comprises natural calcium carbonate.
Optionally, the calcium carbonate is present in an amount in the range 10% to 35% by weight of the composition.
Optionally, the abrasive silica comprises silica with a mass median diameter in the range 3 to 4 μm.
Optionally, the abrasive silica is present in an amount in the range 3% to 25% by weight of the composition.
Optionally, the composition thither comprises at least one additional ingredient selected from the group consisting of surfactants, desensitising agents, whitening agents, tartar control agents, binders, thickening agents, detergents, adhesion agents, foam modulators, pH modifying agents, mouth feel agents, sweeteners, flavourants, colourants, preservatives, humectants, fluoride sources and combinations thereof.
In a second aspect, the invention provides an oral care kit comprising the dentifrice composition.
In a third aspect, the invention provides the use of the composition in tooth whitening.
In a fourth aspect, the invention provides a method of polishing tooth enamel comprising applying the composition to the surface of the enamel.
It has surprisingly been found that, by incorporating calcium carbonate into a tooth whitening composition based on abrasive silica it was possible to increase zinc uptake. This enables enhanced antibacterial, anticavity, enamel erosion protection, breath fresheners and other benefits in tooth-whitening compositions.